This invention relates to document feeding apparatuses and, more particularly, to bottom level sheet feeding apparatuses.
Many modern, high speed copiers are capable of copying serially paginated booklets and the like, one page at a time, and presenting the copies as well as the copied pages in the proper sequential order. To accomplish this function, such devices commonly utilize bottom level document feeders which receive a stack of original documents to be copied, remove the lowermost sheet from the stack and convey it to the copying station. The advantage of a bottom level document feeder is that successive stacks of original sheets may be loaded into it, even as the sheets are being withdrawn from the lowermost stack, and the resultant copies and originals are presented in the same order in which they were loaded into the device.
There are many types of bottom level documents feeders. For example, Strobel, Jr., U.S. Pat. No. 3,934,869 discloses a bottom level document feeder which includes a stack receiving tray, an endless belt conveyor partially extending into the tray, an abutment plate located downstream of the tray and above the belt, and a retard pad located above the belt and downstream of the abutment plate. The abutment plate is oriented substantially perpendicularly to the portion of the belt conveyor which contacts and transports the sheets loaded onto the tray. The conveyor includes an idler roller located slightly upstream of the abutment plate.
In operation, the conveyor urges a stack of sheets loaded onto the tray forwardly until their leading edges contact the vertical abutment plate. A gap beneath the plate allows the conveyor to displace a lowermost sheet or sheets forwardly beneath the abutment plate and into contact with the retard pad. The retard pad has a coefficient of friction sufficient to hold and thereby separate any additional sheets carried through the opening from the lowermost sheet and prevent their moving further with the lowermost sheet. Thus, only the lowermost sheet is conveyed past the retard pad by the belt, which has a coefficient of friction higher than that of the retard pad and thus can convey a sheet of paper past the retard pad.
Another example of a bottom level document feeder is disclosed in the Kramell et al. U.S. Pat. No. 3,895,791. This sheet feeder comprises an in-feed chute which preferably is sloped between 40.degree. and 60.degree. to the horizontal, a belt positioned the chute and extending into a paper feeding tray, an intermediate roller positioned beneath the chute, and a retard pad positioned downstream of the chute. The in-feed chute of this device does not form a pinch point with the conveyor since it is pivotally mounted to the machine supporting the belt and rollers, and therefore can pivot upwardly away from the sheets being fed. A weight is mounted on the in-feed chute to urge it downwardly so that only a lowermost sheet or sheets is conveyed by the belt beneath the in-feed chute to the retard pad.
A problem inherent with many bottom level document feeding apparatuses is that the conveying means for transporting the lowermost sheet from the stack within the paper tray often conveys more than a single sheet so that a number of sheets pass the abutment plate located downstream of the paper tray and are conveyed past the retard to the station. This results in misfeeds and requires the sheet feeding operation to be stopped and the excess sheets removed from the apparatus downstream of the stack. An excessive number of such misfeeds results in significant downtime of the entire copying or duplicating machine, and possibly an unacceptable number of copy sheets which have either no text at all imprinted upon them, or text which is misregistered.
Accordingly, there is a need for a bottom level document feeding apparatus which is relatively simple and economical to manufacture and service. There is also a need for a bottom level document feeding apparatus which is relatively reliable in that it rarely allows more than the lowermost sheet of a stack to be removed therefrom and transported to a next subsequent station.